1. Field of the Invention
This invention relates to polypeptides that are mutated to contain a salvage receptor binding epitope. More particularly, this invention relates to polypeptides that are cleared through the kidney having an epitope from the Fc region of an IgG molecule, resulting in longer circulatory half-life.
2. Description of Related Literature
It was proposed in 1964 that a specific receptor exists in rapid equilibrium with the intravascular space that protects IgG molecules from degradation. Brambell et al., Nature, 203: 1352-1355 (1964). See also Brambell, The Lancet, 1087-1093 (1965). The kidney has been shown to be the major site of catabolism of immunoglobulin fragments, according for approximately 90% of their endogenous catabolism. Wochner et al., J. Exp. Med., 126: 207(1967). The existence of a receptor implies that the Ig molecule has specific sequences, or conformational determinants, that must bind to such a receptor. Since the Fc region of IgG produced by proteolysis has the same in vivo half-life as the intact IgG molecule and Fab fragments are rapidly degraded (Spiegelberg and Wiegle, J. Exp. Med., 121: 323-338 1965!; Waldmann and Ghetie, "Catabolism of Immunoglobulins," Progress in Immunol., 1: 1187-1191 Academic Press, New York: 1971!; Spiegelberg, in Advances in Immunology, Vol. 19, F. J. Dixon and H. G. Kinkel, eds. Academic Press, N.Y.: 1974!, pp. 259-294; and reviewed by Zuckier et al., Semin. Nucl. Med., 19: 166-186 1989!), it was believed that the relevant sequences of mouse IgG.sub.2b were in the CH2 or CH3 domain and that deletion of one or the other domain would give rise to rapid degradation. In fact, the CH2 domain fragment of human IgG produced by trypsin digestion of the Fc fragment persisted in the circulation of rabbits for as long as the Fc fragment or IgG molecule; in contrast, the CH3 domain (pFc') fragment of human IgG also produced by trypsin digestion of the Fc fragment was rapidly eliminated, indicating that the catabolic site of IgG is located in the CH2 domain. Ellerson et al., J. Immunol., 116: 510 (1976); Yasmeen et al., J. Immunol., 116: 518 (1976). Other studies have shown that sequences in the CH3 domain are important in determining the different intravascular half-lives of lgG.sub.2b T and IgG.sub.2a h antibodies in the mouse. Pollock et al., Eur. J. Immunol., 20: 2021-2027 (1990).
The catabolic rates of IgG variants that do not bind the high-affinity Fc receptor FcRI or C1q are indistinguishable from the rate of clearance of the parent wild-type antibody, indicating that the catabolic site is distinct from the sites involved in FcRI or C1 q binding. Wawrzynczak et al., Molec. Immunol., 29: 221 (1992). Also, removal of carbohydrate residues from the IgG molecule or Fc fragment has either a minor role in or no effect on the in vivo half-life, and the extent of this effect depends on the isotype of the IgG molecule. Nose and Wigzell, Proc. Natl. Acad. Sci. USA, 80: 6632 (1983); Tao and Morrison, J. lmmunol., 143: 2595 (1989); Wawrzynczak et al., Mol. Immunol., 29: 213 (1992).
Staphylococcal protein A-IgG complexes were found to clear more rapidly from the serum than uncomplexed IgG molecules. Dima et al., Eur. J. Immunol., 13: 605 (1983). To determine if residues near the Fc-SpA interface are involved in IgG clearance, Kim et al., Eur. J. Immunol., 24: 542-548 (1994) performed site-directed mutagenesis to change amino acid residues of a recombinant Fc-hinge fragment derived from the murine immunoglobulin G1 molecule and determine the effects of these mutations on the pharmacokinetics of the Fc-hinge fragment. The authors showed that the site of the IgG1 molecule that controls the catabolic rate (the "catabolic site") is located at the CH2-CH3 domain interface and overlaps with the Staphylococcal protein A binding site. See also WO 93/22332 published Nov. 11, 1993. The concentration catabolism phenomenon is also studied in Zuckier et al., Cancer, 73: 794-799 (1994). IgG catabolism is also discussed by Masson, J. Autoimmunity, 6: 683-689 (1993).
WO 94/04689 discloses a protein with a cytotoxic domain, a ligand-binding domain and a peptide linking these two domains comprising an IgG constant region domain having the property of increasing the half-life of the protein in mammalian serum.
A stereo drawing of a human Fc fragment and its complex with fragment B of Protein A from Staphylococcus aureus is provided by Deisenhofer, Biochemistry, 20: 2364 (1981).
It has been shown that clearance is greatly reduced when the effective molecular size exceeds 70 kDa, the glomerular filtration cutoff size. Knauf et al., "Relationship of Effective Molecular Size to Systemic Clearance in Rats of Recombinant lnterleukin-2 Chemically Modified with Water-soluble Polymers," J. Biochem., 263: 15064-15070 (1988).